The present application relates generally to steam turbines, and more particularly, to systems for reducing the level of erosion experienced by steam turbine components.
Low-pressure steam turbines are typically driven by wet steam, the moisture content of which may have the form of water film or water droplets. This moisture causes efficiency losses and potential erosion of steam turbine components. This erosion is most prominent in steam turbine airfoils/blades as the moisture content of the steam impacts the nozzles (stationary airfoils) or buckets (rotating airfoils). The erosion is even more exaggerated in some last stages of steam turbines, where speed and local wetness values are highest.
Several solutions have been proposed to reduce the amount and/or size of water droplets accumulated on steam turbine components. One solution adds radial grooves close to the leading edge of rotating airfoils to remove the deposited moisture. These grooves, however, only remove moisture that has already caused significant efficiency losses to the rotating airfoils and upstream stationary airfoils. Other solutions rely on protective measures, which include water removal through water drainage arrangements in outer sidewalls (end walls) of the nozzle; or through suction slots made in hollow stator airfoils. This moisture is then collected in circumferential cavities between the diaphragm and the casing and drained to a condenser.
These moisture removal concepts are based on extraction of moisture film from blade surfaces, through slots, driven by the pressure drop between the steam path and the hollow blade inner space. This pressure drop causes a significant amount of steam to pass through the hollow stator blades and into the condenser. This decreases the steam turbine efficiency.
Another recently developed technique extracts moisture from blade surfaces through multiple extraction bores in the airfoils. There, the extracted moisture is led to an external steam/moisture separator, the separated water is drained, and the steam is returned back to the main steam path through a steam injection bore located in the center of the pressure side. This technique provides moisture removal as well as steam reinsertion into the steam path, thus improving steam turbine efficiency. There remains, however, room for improvement in providing further structures aimed at reducing blade erosion.
As a result, there is a desire for improved systems for efficiently and cost effectively reducing moisture-related issues in steam turbine components, such as efficiency losses and potential erosion.